Titleist actually prints an expensive brochure titled The Best Ball for Your Game to promote the concept of ball fitting. Since Titleist is the #1 Ball in golf, (an inside joke in our house since we've all been brainwashed to believe that) it's in their best interest to convince you, the golfer, that ball fitting matters.
In fact, there are substantial differences between one ball and another that even a mid-handicapper can notice, especially a golfer who plays a lot. These differences mostly show up off the driver, wedge and putter face.
The best place to test golf balls is on the course, but who has time for that? We can figure out when a ball doesn't get in the air or land the way we expect, when it doesn't go the distance or gets scuffed too easily, but how do we know when it's the ball or the club, or the swing?
Back spin, side spin and carry, all factors associated with the golf ball, can be measured on a launch monitor. These characteristics are helpful to know when you use your driver, irons and wedges.